This invention relates to printed circuit board (PCB) based antennas.
Yagi antennas are used for various high-frequency applications such as the reception of television signals, point-to-point communications, and certain types of military communications. The Yagi antenna is typically made up of linear wire or rod-type elements, each having a length of approximately 1/2  wavelength. These elements are arranged in a row, with each element parallel to each other. The rear element in this array is called the reflector. The second element is the driven element, which is connected to the transmission line, and all other elements in front of the driven are called directors. The directors are typically positioned along an antenna axis with the directors extending in the transmission direction from the dipole. The transmission direction is that direction to which electromagnetic energy is to be transmitted, or from which signal energy is to be received. The gain of a single Yagi antenna ranges from about 6 to 20 dBi, depending upon the length of the array. Multiple Yagi antennas may be connected together side by side in larger arrays.
U.S. Pat. No. 5,061,944, the content of which is incorporated by reference, discloses the use of parasitic elements to allow the array of directors on the antenna axis to be about 25% shorter than would otherwise be required. Parasitic arrays can also be placed parallel to and adjacent to the distal end of the main array on the antenna axis to improve the directivity of the antenna, as is disclosed in U.S. Pat. No. 3,218,645. The described antenna is the to provide an increase in gain of 60%, which is equivalent to a decrease in length of about 38% compared to a standard Yagi antenna for the same gain. To provide even shorter antennas for the same gain, U.S. Pat. No. 5,612,706, the content of which is incorporated by reference, discloses a driven element disposed on an antenna axis for transmission of electromagnetic energy in a transmission direction along the antenna axis. First and second parasitic arrays are disposed on opposite sides of the antenna axis in the transmission direction from the driven element. At least a portion of the antenna axis adjacent to the parasitic arrays is without parasitic elements. Each parasitic array has a plurality of parallel parasitic elements or directors spaced apart along a respective array line that includes a proximal portion adjacent to the driven element that extends in a general direction that is at an acute angle to the transmission direction. The first and second parasitic arrays are sufficiently close to the antenna axis to produce a radiation pattern that has a lobe with greatest magnitude in the transmission direction.
The proper installation of a Yagi antenna typically requires the use of a signal strength indicator and/or external measurement equipment. An installer must aim the antenna at the time of installation. If a new transmitter site becomes available, the installer may have to revisit the site to reorient the antenna to take advantage of the stronger, closer transmitter. Hence, in addition to high material and assembly cost, Yagi antennas are also labor intensive during installation.
To minimize material and labor costs, U.S. Pat. No. 6,046,703, the content of which is incorporated by reference, discloses a wireless transceiver that includes a dielectric substrate having first and second major surfaces on which an RF circuit and a baseband processing circuit are mounted, and a printed circuit antenna formed on the substrate. The printed circuit antenna has at least one director formed by strip conductors disposed on the substrate, a reflector formed by the edge of a ground area disposed on the substrate, and a radiating element formed by strip conductors on the substrate. The radiating element is positioned between the reflector and the director.